Laser guidance systems for controlling guided missiles or other remotely controlled vehicles are known in the art. For example, in a conventional laser guided missile, a laser is used to illuminate the desired target. The laser may be mounted on the missile itself, or may be directed at the target from a separate ground or air-based source. In either case, the laser energy is reflected from the target and detected by the missile. The missile then uses this energy to determine the direction to the target and navigate towards it.
To detect the reflected laser energy, the missile typically has a number of apertures arranged in its nose or other areas on the missile surface. Lenses or other optical components are often located in the apertures to assist in the collection to of the reflected laser energy. The reflected laser energy received at the apertures is then directed into fiber optic cables that transmit the reflected laser energy into detectors mounted within the missile. These detectors convert the laser energy into electrical signals that are then passed to the missile's onboard computer system. The computer system then uses these signals to determine the direction to the target and guide the missile accordingly.
The amount of energy in the electrical signals is, of course, proportional to the corresponding amount of laser energy received on the fiber optic cables. Because the fiber optic cables correspond to different apertures on the missile, the amount of energy in the fiber optic cables will vary depending on the angle from which the energy was received. Therefore, by knowing the arrangement of the apertures, and which apertures correspond to particular fiber optic cables, it is possible to compare the relative amount of energy from each of the fiber optic cables to determine the direction from which the received laser energy is coming from.
Therefore, for the guidance computer to accurately determine the direction to the target, it is important that the signals provided by the detectors accurately reflect the relative amount of laser energy received at their respective apertures. But the gain or responsivity is not necessarily uniform between detectors. Typically, detectors are manufactured having a specified tolerance or variation in their gain or responsivity to laser energy. Therefore, at the factory these variations are normally measured and stored in the memory of the missile's computer system for each detector. This allows the missile's computer system to compensate for the variations in detector responsivity when it compares the relative amounts of energy received at the apertures. However, the variation in detector responsivity may also vary with such factors as temperature or the voltage that is applied to the detectors. This leads to errors in determining the relative amount of energy received at each aperture on the missile, which, in turn leads to errors in navigation.